is it an obligation to say Chazarat HaShatz even if everyone there knows how to say it by themselves, that is what he Chachamim set it up. It is also forbidden to be busy with other things during Chazarat HaShatz except to look in the siddur and focus on what the Chazzan is saying and answer Amen.
Explanation:
There is a cryptic Mishna in Rosh Hashanah 33b: Just as the Shliach Tzibur is obligated so too every single individual is obligated. Rabban Gamliel said The Shliach Tzibur can fulfill the Tzibur’s obligation for them.
The Gemara (34b) explains this Mishna: Rabban Gamliel says that the Chachamim according to you why do we have a Shliach Tzibur at all, he is unneeded. The answered him it’s in order to exempt those who don’t know the tefilla and to give them the mitzvah, and just as he exempts those who don’t know he also can exempt those who know.
We rule like the Chachamim a sit says in Shulchan Aruch 124:1: After the Tzibur finishes the Tefilla the Shliach Tzibur should repeat the Tefilla in case there were those who didn’t know they should focus on what he is saying, and he fulfills their mitzvah.”
It is true the original reason for Chazarat HaShatz was or those who didn’t know the tefilla, but it matters less.
The Abudraham quotes the Teshuvat HaRambam (Pee’r Hador 148) who was asked,” A congregation which prayed and all of them know the Tefillot, is there a need for a Shliach Tzibur to go to the amud and say Chazarat HaShatz out loud?”
The Rambam answers, “Since the Chachamim decreed that there must be a Shliach Tzibur to pray for those who don’t know the Tefilla, Chazarat HaShatz is not considered a Bracha Levatala (a useless bracha) even if everyone knows, like the Gemara in Pesachim which said that they also decreed to make Kiddush in the Bet HaKnesset. Even though the main decree was for guests who did not have a place, still all Batei Knesset say it even if there are no guests. It is also like the Bracha we say after Shemoneh Esrei on Shabbat night (M’ein Sheva) for those who came late to the Bet Knesset and yet we are always required to say it even if everyone is there. So too every decree which was set up for a reason even if the reason doesn’t apply it was set in case it would occur. This important because otherwise The Chachamim’s decrees vary according to circumstance, and every Tefilla one would have to test every person in the Minyan if they know Tefilla.”
So even today we are required to say Chazarat HaShatz. So ruled the Shulchan Aruch 124:3,” A Kahal which preyed and all of them know the Tefilla even still the Shliach Tzibur should go to the Amud and repeat the Tefilla to fulfill the decree of the Chachamim.”
Whether one is permitted to learn from Seforim during the Chazara is an old Machloket. The Magen Avraham 124:8 quotes the Teshuvot Menachem Azaria (Ram “a Mipano) who says that those men who learn Torah during the Chazarat HaShatz, if they answer every bracha there is no need to protest.
The Vavei HaAmudim protests strongly. The Magen Avraham agrees to the Vavei HaAmudim, for different reason though. He brings a proof from the halacha in the Rema (90:18) that someone who is Torato Umanato (He learns Torah every second and doesn’t stop learning for anything) is exempt from praying with a minyan because the of the extra time it takes from his learning. However, the Rema writes that one should not actually do this regularly so that simple people should not learn from your example and not go to Bet Knesset (Hey if the big Rabbi doesn’t go to Minyan, why should I). Even more so he should learn in the Bet Knesset instead of saying Selichot or Tachanun.”
So rules the Mishna Berura 124:17: that if people learn during the Chazarat HaShatz then simple people will learn from them not to pay attention during the Chazarah as well and talk (or read their texts or emails) and they are causing the many to sin.” Therefore, one should not learn anything and focus on what the Shliach Tzibur says and answer Amen. (In a Yeshiva there might be more room to be lenient, but one must ask the Rosh Yeshiva.)
